Background

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ISO 8601

ISO 8601:2004 "Data elements and interchange formats – Information interchange – Representation of dates and times is an international standard covering the exchange of date and time-related data. It was issued by the International Organization for Standardization (ISO) and was first published in 1988. ... In general, ISO 8601 applies to representations and formats of dates in the Gregorian (and potentially proleptic Gregorian) calendar, times based on the 24-hour timekeeping system (including optional time zone information), time intervals and combinations thereof." (Wikipedia)

It "is applicable whenever representation of dates in the Gregorian calendar, times in the 24-hour timekeeping system, time intervals and recurring time intervals or of the formats of these representations are included in information interchange. ..."